and explanation is definitely known. 



2. Salinity 



The salinity values derived from water samples collected in the 

 Weddell Sea area were generally typical for the Antarctic Regions. 

 Figure 3 illustrates the salinity structure obtained from a series 

 of oceanographic stations across Drake Passage. Surface salinities 

 were variable, averaging about 34.00 °/oo (between 33.89 °/oo and 

 34.26 °/oo)« Salinities increased with depth, but the gradient was 

 much shallower and somewhat sharper south of the Antarctic Convergence 

 than north of it because the warm, deep water that rises in the region 

 of the convergence also contained a greater salinity than the surround- 

 ing waters. The salinity maximum that originated in the warm, deep 

 water is maintained in the Antarctic Circumpolar Water and is gener- 

 ally 34.70 °/oo or higher (Fig. 4). However, the salinity gradient 

 below this maximum is very gradual and this zone of transition and 

 vertical mixing makes it difficult to determine where the Antarctic 

 Bottom Iflfeter is definitely encountered. 



Surface salinity values within the Weddell Sea itself are gener- 

 ally higher than to the north. However, many exceptions to this 

 statement are found as melting glacial, shelf, or old pack ice decreases 

 the surface salinity and the freezing sea water releases salt, increasing 

 the salinity. Local conditions of precipitation versus evaporation 

 also contribute to surface salinity fluctuations. 



The salinity structure for a typical siumner station over the Weddell 

 Shelf is illustrated by Station S.I. -24. Extensive pack ice prevented 

 extensive surface diluting through melting. 



3 . Density 



Figure 3 is a profile of density values across Drake Passage. 

 Densities generally increased southward and with depth. The density 

 increase southward results from the climatic decrease in temperatures 

 southward. The density increase with depth predominantly results from 

 a temperature decrease north of the Antarctic Convergence, and from a 

 salinity increase south of the convergence. 



Near the pack ice areas of the Weddell Sea, and within the sea it- 

 self, the surface densities varied with the surface temperature fluc- 

 tuations, and the corresponding melting or freezing conditions of the 

 pack of glacial ice. Melting conditions quickly lower and stabilize 

 surface densities, both from higher temperatures and from the release 

 of fresh water to the surface layers. Conversely, freezing conditions 

 lower temperatures and separate salt ions from the sea water, thus 

 causing an increase in density. This often creates a temporary imstable 

 condition, with denser water at the surface; however, vertical mixing 

 soon stabilizes the situation, deepening the isopycnal layer. In the 



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